1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and more particularly relates to a treatment of a back surface of a GaAs substrate on which a semiconductor device is formed.
2. Related Background Art
A semiconductor element formed on a GaAs Substrate, a chemical compound semiconductor, has a difficulty to dissipate heat generated from the device formed on a surface of the GaAs substrate, since thermal conductivity of GaAs is 1/3 times as low as that of Si. It adversely affects characteristics of the device. And, it is necessary to thin the substrate and assure a good dissipation of heat. On the other hand, GaAs is brittle compared with Si and easy to be cracked and/or broken off. So, chip cracking is easily caused starting from fine flaws and the like yielded at a thinning process. Therefore, mirror surface finish has been conventionally adopted with a grinding stone having fine grain sizes (See "THE IMPACT OF WAFER BACK SURFACE FINISH ON CHIP STRENGTH" of IEEE/IRPS). And, an application filed by the assignee and inventor of the present invention on Dec. 5, 1986 also disclosed that GaAs substrate has the maximum strength after die-bonding when back finish (R max) of the substrate is somewhat between 0.2 and 0.5 micro-meters. It is, however, difficult to obtain R max in this region only with grinding. And, in the prior art, mirror grinding has been used to obtain R max of 0.1 micro-meters or finer to eliminate fine flaws, consequently preventing a chip from being cracked.
A grinding stone with fine grains, however, must be used to perform the aforementioned mirror grinding. It means only a small amount to be ground off per a unit time and taking a long time of period to grind off a predetermined amount. It results in low productivity for mass production and in making a process complicated because of a need of facilities for mirror grinding.